1. Field of the Invention
The invention relates to a high velocity flame jet apparatus. More particularly, the invention relates to a high velocity flame jet burner for thermoabrasive cutting or cleaning or for applying protective coatings.
2. State of the Art
High velocity flame jet apparatuses are used for blast cleaning, abrasive cutting of rock and other solids, and for the atomization of liquids. These devices generally include a combustion chamber in which a combustible fluid such as kerosene is ignited, conduits for delivering air, combustible fluid, and particles to the combustion chamber, and an outlet nozzle through which particles exit at supersonic speed. The particles may be abrasive particles for cleaning or cutting or powder particles for protective coating.
High velocity flame jet apparatuses are used for cutting concrete, stone, steel, aluminum and other hard materials. They are also used for cleaning highways, runways, and various construction materials to remove organic deposits, corrosion and paint. In addition, these apparatuses are used to apply protective coatings of various materials to large surfaces. High velocity flame jet apparatuses are also often used under water.
A typical high velocity flame-jet apparatus is shown in U.S. Pat. No. 4,384,434 to Browning. Browning teaches an apparatus in which compressed air and abrasive particles are delivered through a single conduit to a "sand separator". The sand separator directs the abrasive particles into the combustion chamber and channels the air into an annular space around the combustion chamber and into the combustion chamber downstream of the particles. As the compressed air flows through the annular space it is heated to a temperature which will vaporize liquid fuel which is injected into the combustion chamber upstream of the air inlet. Browning's device has the advantage that air and abrasive particles may be conducted to the combustion chamber via a single conduit. However, in order to make effective use of the sand separator, the particles must be relatively large. This often requires sifting the particles before using them in the apparatus. In addition, the Browning ignition system requires that the combustion chamber be fitted with an oxygen conduit. One of Browning's embodiments injects combustible products in a direction perpendicular to the gas flow. This reduces the axial speed of the particles and produces extra wear on the apparatus. If the particles are protective coating, however, this arrangement results in the unnecessary coating of the inside of the apparatus reducing its useful lifespan. Moreover, Browning's arrangement results in the particles being heated in the combustion chamber which can reduce their hardness and thus their abrasive properties.